For all participants, right after one regular treatment fraction, NeuroPET or NeuroPET II will be wheeled into the patient room. The patient bed will be moved directly into the scan position and a PET scan will be acquired in list-mode for 15 to 20 minutes followed by a CT scan for ~5 minutes. After undergoing their first PET scan, participants will have the option to undergo 1-2 additional scans throughout radiation treatment in the same manner as the first scan.